1. Technical Field of the Invention
This invention relates to a multistage distillation method for the purification of a methyl tertiary butyl ether reaction product comprising methyl tertiary butyl ether, tertiary butyl alcohol, methanol, isobutylene and water wherein the methyl tertiary butyl ether reaction product is charged to a recovery zone comprising a plurality of distillation columns, each of which is equipped with a reflux condenser and a reboiler and wherein the methyl tertiary butyl ether reaction product is separated in a primary methyl tertiary butyl ether distillation column into a lower boiling methyl tertiary butyl ether distillation fraction and a higher boiling aqueous tertiary butyl alcohol fraction, wherein the higher boiling aqueous tertiary butyl alcohol fraction is separated in a tertiary butyl alcohol distillation column into a vaporized overhead tertiary butyl alcohol fraction and a higher boiling water fraction, wherein cooling water is charged to the reflux condenser for the tertiary butyl alcohol distillation column to liquify the vaporized, overhead tertiary butyl alcohol fraction and to convert the cooling water to low pressure level steam, and wherein low level steam generated in said reflux condenser for said tertiary butyl alcohol distillation column is charged to the reboiler for the primary methyl tertiary butyl ether distillation zone to supply the heat necessary for the distillation to be effected therein.
2. Prior Art
It is known to separate mixtures of organic hydrocarbons such as those present in an organic hydrocarbon reaction product by staged distillation in a distillation train comprising two or more distillation columns. Distillation columns conventionally utilize a reboiler to heat a bottoms stream to provide the thermal energy required for the distillation and a reflux condenser for condensing the vaporized overhead fraction withdrawn from the top of the distillation column. It is conventional in multistaged distillation to supply thermal energy to one distillation column by passing the hot overhead vapor or liquid distillation product from another distillation column through the reboiler heat exchanger so that the reboiler heat exchanger functions simultaneously as a reboiler for one column and as a reflux condenser for another column.
That is to say, the conventional method of heat integration is to employ condensers in one column as reboilers in another. The main drawback of the direct coupling of column exchangers is that the columns become closely coupled in duty and operation. Although minor changes in temperature and reflux rates can be accommodated by adjustment of the reflux condenser, significant changes in the operation of one of the columns inevitably upsets the other in return. For example, start-up and shut-down operations become complicated and tricky because all of the associated equipment must be manipulated simultaneously. Also, to avoid control interactions due to changes in liquid level, the reboilers columns generally must be elevated above the receiver of the heat supplier column. This contributes significantly to construction costs and maintenance costs.
It is known to generate steam in a cumene distillation column for use as a heating medium for a reboiler of a phenol distillation column.